Poloidal asymmetry of turbulent fluctuations in the torsatron TJ-K

In order to get insight into the spatial structure of turbulent fluctuations on an inner flux surface of a toroidal plasma, measurements with a poloidal probe array were carried out in the torsatron TJ-K. A local maximum in fluctuation levels and net transport was found on the LFS of the magnetic configuration, where bad curvature gives rise to enhanced instability. In this region, wavelet analysis carried out on the data revealed an increase in the cross-phase φ_nφf of density and potential fluctuations. Though drift-wave turbulence is still dominant, the increase in φ_nφ might point to a contribution of curvature drive to the instability. On the LFS, high fluctuation power appears together with increased φ_nφ and on the HFS, low power together with lower φ_nφ. However, the poloidal position of maximum transport is subject to a displacement from the LFS, which could be related to background E xB flow. Indeed, at magnetic-field reversal, the displacement changed sign (but also magnitude). The understanding of this effect is subject of future investigations and could be of special importance with regard to scrape-off layer transport or interpretations of results from single point measurements.